Sharing Physically Based Materials Between Renderers with MDL Jan Jordan Software Product Manager MDL March 18, GTC San Jose 2019 Lutz Kettner Director Advanced Rendering and Materials
Introduction to NVIDIA Material Definition Language MDL Matching the appearance of a single material within different rendering techniques Agenda Defining physically-based materials MDL ecosystem Become part of the ecosystem 2
Introduction 3
The NVIDIA Material Definition Language (MDL) is technology developed by NVIDIA to define physically-based materials for physically-based rendering solutions. 4
5 Iray Photoreal
6 Iray Photoreal
7 Iray Photoreal
courtesy Harley Davidson 8
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11 NVIDIA vMaterials with Iray Photoreal
12 Iray Photoreal
MDL in Substance Designer 13
14 Substance Designer
Matching the Appearance of a Single Material Within Different Rendering Techniques 15
One Scene for Different Renderers Realtime Rasterizer Interactive Raytracer Pathtracer Share scene and Switching renderers MDL materials for a with no scene consistent look modifications 16
Iray Photoreal Iray Interactive Iray Realtime 17 Path Tracer Ray Tracer, Direct Illumination OpenGL Rasterizer
Traditional Shading Language Parts Material Material Texturing Definition Implementation Texture lookups Glossy reflection Light loops / trace N rays Procedurals Transparency OIT / ray-continuation Uv-transforms Translucency Ray marching Projectors Noise functions Math functions 18
Renderer Procedural Program- Declarative Material Rasterizer ming Language Definition Light loops / OIT Texture lookups Glossy reflection Raytracer Procedurals Transparency Uv-transforms Translucency Trace N rays Projectors Pathtracer Noise functions Math functions Ray-marching 19
Renderer Procedural Program- Declarative Material Rasterizer ming Language Definition Light loops / OIT Raytracer Trace N rays Pathtracer Ray-marching 20
Renderer Procedural Program- Declarative Material Rasterizer ming Language Definition Light loops / OIT MDL is not a Shading Language Raytracer MDL defines what to compute, not how to compute it Trace N rays – no programmable shading – no light loops or access to illumination Pathtracer – no trace call – no sampling Ray-marching – no camera dependence 21
MDL Material Model material surface volume geometry backface … 22
MDL Material Model material surface volume geometry scattering bsdf backface … 23
MDL Material Model material surface volume geometry scattering bsdf emission emission edf intensity backface … 24
MDL Material Model material surface volume geometry scattering scattering vdf bsdf scattering_coefficient emission absorption_coefficient emission edf intensity backface … 25
MDL Material Model material surface volume geometry scattering scattering displacement vdf bsdf cutout_opacity scattering_coefficient emission normal absorption_coefficient emission edf intensity backface … 26
MDL Material Model material surface volume geometry scattering scattering displacement vdf bsdf cutout_opacity scattering_coefficient emission normal absorption_coefficient emission edf intensity backface … ior thin_walled 27
MDL Elemental Distribution Functions Bidirectional Scattering Distribution Functions Diffuse Reflection Diffuse Transmission Glossy (various) Backscatter Glossy Specular Reflection Spec. Refl.+Transm. Measured BSDF 28
MDL Elemental Distribution Functions Emissive Distribution Functions Diffuse Spot IES Profile Volume Distribution Functions Henyey-Greenstein 29
MDL Distribution Function Modifiers Tint Thin Film Directional Factor Measured Curve Factor 30
MDL Distribution Functions Combiners Normalized Mix Fresnel Layer Clamped Mix Custom Curve Layer Weighted Layer Measured Curve Layer 31
MDL Layered Material Example 32
Defining Physically-based Materials With Source Code 34
Defining a Material Using MDL MDL is a ‘C’ like language. The material viewed as a struct struct material { bool thin_walled ; material_surface surface ; material_surface backface ; color ior ; material_volume volume ; material_geometry geometry ; }; 35
Defining a Material Using MDL MDL is a ‘C’ like language. The material and its components viewed as a struct struct material { bool thin_walled; material_surface surface; material_surface backface; color ior; material_volume volume; material_geometry geometry; }; struct material_surface { bsdf scattering; material_emission emission; }; 36
Defining a Material Using MDL MDL is a ‘C’ like language. The material and its components viewed as a struct struct material { bool thin_walled = false ; material_surface surface = material_surface() ; material_surface backface = material_surface() ; color ior = color(1.0) ; material_volume volume = material_volume() ; material_geometry geometry = material_geometry() ; }; struct material_surface { bsdf scattering = bsdf() ; material_emission emission = material_emission() ; }; 37
Defining a Material Using MDL Material struct is already fully defined material(); 38
Defining a Material Using MDL Material struct is already fully defined material(); 39
Defining a Material Using MDL Creating new materials material name ( material-parameters ) = material ( material-arguments ); 40
Defining a Material Using MDL material plaster( ) = material( surface : material_surface( scattering : df:: diffuse_reflection_bsdf () ) ); 42
Defining a Material Using MDL New materials can have parameters material plaster ( color plaster_color = color(.7) ) = material( surface: material_surface ( scattering: df::diffuse_reflection_bsdf ( tint: plaster_color ) ) ); 43
Defining a Material Using MDL Create complex materials by layering material plastic( color diffuse_color = color(.15,0.4,0.0), float roughness = 0.05 ) = material( surface: material_surface( scattering: df::fresnel_layer ( ior: color(1.5), layer: df::simple_glossy_bsdf ( roughness_u: glossy_roughness ), base: df::diffuse_reflection_bsdf ( tint: diffuse_color ) ) ) ); 44
MDL Handbook www.mdlhandbook.com January 10th update: more on procedural texturing and displacement Upcoming: advanced volumes 46
MDL Procedural Programming Language C-like language for function definitions Function results feed into material and function parameters “Shader graphs” are equivalent to function call graphs texture_coordinate texture_space`: 0 summed_perlin_noise position color_constructor value Material plaster plaster_color 47
Defining a Function Using MDL Functions allow control flow like loops, switches, conditionals float summed_perlin_noise ( float3 point, int level_count=4, float level_scale=0.5, float point_scale=2.0, bool turbulence=false) { float scale = 0.5, noise_sum = 0.0; float3 level_point = point; for (int i = 0; i < level_count; i++) { MDL Handbook float noise_value = perlin_noise(level_point); if (turbulence) noise_value = math::abs(noise_value); else noise_value = 0.5 + 0.5 * noise_value; noise_sum += noise_value * scale; scale *= level_scale; level_point *= point_scale; } return noise_sum; } 48
Defining a Function Using MDL Call graph of functions substitute shader graphs texture_coordinate material perlin_noise_material() texture_space`: 0 = plaster ( summed_perlin_noise plaster_color: color ( position summed_perlin_noise ( point: state:: texture_coordinate(0) color_constructor ) value ) Material plaster ) plaster_color 49
MDL Module System MDL is program code MDL is a programming language allowing dependencies among modules and materials import nvidia::vMaterials::Design::Metal::chrome::*; We use search paths to resolve imports 50
MDL Module System MDL is program code MDL is a programming language allowing dependencies among modules and materials import nvidia::vMaterials::Design::Metal::chrome::*; We use search paths to resolve imports C:\Users\Jan\Documents\mdl\nvidia\vMaterials\Design\Metal\chrome.mdl MDL package space search path nvidia::vMaterials::Design::Metal::chrome 51
MDL 1.5 Preview MDL Encapsulated File Format (MDLE) refactor main.mdl MDL SDK .mdl resources/… .jpg .mdle unpack .jpg .mdl thumbnails/… One material – fully self contained in one file Includes textures, previews, etc. in the file Renaming and copying works … work just like textures 52
MDL 1.5 Preview Internationalization (i18n) Localization of all MDL string annotations Based on OASIS standard XLIFF 1.2: XML Localisation Interchange File Format http://docs.oasis-open.org/xliff/xliff-core/xliff-core.html Package and module XLIFF files in MDL file hierarchy Example C:\Users\%USERNAME%\Documents\mdl\ MDL search path nvidia\vMaterials\fr.xlf French vMaterial package XLIFF file nvidia\vMaterials\AEC\Glass\Mirror_fr.xlf French Mirror module XLIFF file 53
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